GB1419981A - Percussion drills - Google Patents

Abstract

1419981 Percussion tools HALIFAX TOOL CO Ltd 28 Nov 1973 [9 Jan 1973] 1142/73 Heading B4C [Also in Division E1] A percussion drill comprises a drill body 1 having a chuck 4 adapted to hold the shank of a drill bit or drill stud for limited axial movement relative to the body, a fluid pressureoperated reciprocable hammer piston 3 adapted to deliver blows to the shank 5, and a central tube 21 within the body adapted to engage the shank and follow at least to a limited extent the axial movement of the shank in the chuck 4, the tube having an exhaust outlet, and exhaust ports 23, 24 for communication with cylinder spaces in the body associated with the piston 3 and co-operative with the piston to control reciprocation thereof. The exhaust outlet of the tube 21 communicates with flushing passages 7 in the drill bit 6. A tubular bush 25 attached to the rear end of the central tube co-operates with a fixed spigot 28 in such a manner that the amount of fluid exhausted directly through the central tube, instead of first entering the cylinder, increases as the tube moves forwardly. If the drill bit suddenly becomes unloaded, the tube moves forward to such an extent that insufficient fluid reaches the cylinder to reciprocate the piston. A lost-motion connection causes relative movement between the tube and shank in response to unloading of the bit to uncover drain ports 22 in the tube. The tube is preferably of resilient plastics material.